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Written by Dave Scott
Matching the Best Airplane to Your Flying Skills
Illustrations by the author
As seen in the March 2016 issue of
Model Aviation.


The following information is intended to provide practical guidelines aimed at helping recreational pilots better predict the flying qualities of different airplane types, and the skill levels required to fly them.

Some readers might feel that certain nuances were left out, and some might be upset that the advanced principles that are the stock and trade of professional aerodynamicists are not included. The purpose of this article is not to try to cover every obscure exception or teach aerodynamics, but to condense flight dynamics into simple rules of thumb that an average pilot can easily understand and use to make better airplane choices that will improve his or her opportunities for success.

One of the most frequent information requests that 1st U.S. R/C Flight School receives is for airplane recommendations. Many of these questions arise from the confusion and frustration of trying to make smart buying decisions amid all of the “best” claims and widespread promises that a pilot will soon fly like a pro if he or she purchases model X.

How well an airplane flies depends on the pilot’s skill level and other factors. What an advanced pilot feels is easy to fly, easy to land, and complements his or her flying style, might not prove as easy for an average pilot.

Landing difficulties and flying that falls short of expectations is often because pilots are flying models that aren’t well matched or set up for their skill levels (e.g., a sport pilot looking to fly with greater precision won’t be happy with the results achieved when flying an airplane designed and set up for extreme 3-D).

Because many people base their decisions on recommendations by individuals, often with different skill levels, and/or advertisers claiming that their airplanes will do every trick in the book and yet supposedly are as easy to land as a basic trainer, pilots usually end up attributing their troubles to needing more practice. Instead of questioning whether their issues are inherent to the airplane or the way it’s set up, many pilots continue to fly with mixed results until another model that promises to make them fly better grabs their attention.

The tricky part of choosing the best model has always been matching it to the pilot’s immediate skill level. Keep in mind that any pilot who buys and sets up an airplane outside of his or her comfort zone is actually delaying his or her future aspirations, especially if he or she wrecks it or becomes apprehensive about flying because it’s no fun to fly (and especially no fun to land). Logic dictates that the best airplane and setup complements the type of flying a person most often does.

Although the flight stabilization systems provided with many aircraft help make them easier to fly, as long as the laws of physics and aerodynamics remain constant, model design and setup will continue to be the main factors dictating how well each airplane handles and your ability to make it do what you want—especially when the inevitable shortcomings with the stabilization technology are encountered. In a nutshell, to get the most out of any stabilization system, the airplane must be fundamentally sound.


General Principles

Size: Although airplane design decisions are targeted at achieving specific performance regardless of size, larger aircraft tend to fly better. Larger models appear to fly slower and are easier to see at greater distances, giving a pilot more time to think. But the biggest practical advantage of flying larger models is that they tend to be more stable in turbulent wind, and therefore open up more flying opportunities with better results.

Surface travel: How quickly an airplane responds to control inputs is a function of how fast and how far the control surfaces deflect, regardless of whether the airplane is small or large, or high or low performance. You can seldom go wrong by initially setting up the control surface deflections/travels to the manufacturers’ recommendations.

To fly your best, you must take the initiative to adjust the control surface travels to suit your skill level. In other words, adjust the airplane to your comfort level instead of trying to change your control habits to accommodate the aircraft.

Good aircraft are often faulted or retired because a pilot does not like how the model handles. For some reason, the pilot puts it upon himself or herself to get used to the aircraft and looks for another airplane when the one he or she has been flying proves to no longer be fun to fly.

Ultimately, you primarily determine the control response, and by changing the travels to suit your comfort level, you can immediately start flying with more confidence and building on that success—rather than continuing to fight an airplane that might only be an elevator adjustment away from becoming a joy to fly.

Exponential: After first adjusting the travels/dual rates to suit your immediate skill level, only add more exponential if you feel that the airplane response is too sensitive or touchy around neutral. If your goal is to fly with maximum precision and predictability, don’t hesitate to take some exponential out if any of the controls feel sluggish or if you sense a lack of correlation between your control inputs/intentions and the response of the airplane (aka a “wet noodle” response caused by too much exponential).

Pilots aspiring to fly with precision should strive to use the least amount of possible exponential (10% to 25%) to maintain the direct correlation between the control inputs and the response of the airplane that is so vital to precision flying. To use an analogy, which is easier to drive precisely: a new car with tight linear steering, or an older car with slop in the steering and a non-linear/irregular steering response?

Center of gravity (CG): Where you choose to balance your model impacts how it will handle and how well you will fly it. Choosing to fly with an aft CG (tail-heavy) causes the airplane to be unstable and harder to fly.

Although it’s true that a tail-heavy condition tends to increase maneuverability, as a consequence, the airplane will be less forgiving and require more effort to fly. It won’t matter how well a tail-heavy model flat spins or hovers if you end up tearing off the gear because it’s so difficult to land.

A nose-heavy airplane tends to be more stable, but also loses some maneuverability and can behave differently during speed changes. The best overall performance is usually achieved when airplanes are set up neither tail-heavy nor nose-heavy, aka neutral.

Wing design: Although many factors contribute to an airplane’s characteristic performance, the most influential design factor determining how an aircraft flies is the wing. Because a handful of wing configurations are found on nearly all model airplanes, the general performance, handling qualities, and skill level required to fly them can be anticipated when you grasp an understanding of how different wing types affect performance.

The remainder of this article is aimed at teaching you how to look past the hype and focus instead on the wing configuration to determine what type of performance each airplane will offer, and which is suitable for you.


Basic Trainer Aircraft Features

A well-trimmed and balanced basic trainer is designed to fly slower and feature positive stability. When it is disturbed, it will tend to return to upright level flight. This type is more forgiving in the event of pilot error and allows pilots reasonable periods of hands-off stability when it is upright.

The design features that produce these qualities center around the wing airfoil and thickness, wing area and length, the wing’s location on the fuselage, dihedral, and the wing shape or planform (see Figure 1).




Figure 1: The primary features that make a good basic trainer are a thick, flat-bottom airfoil, high wing placement, and constant chord. The thick, flat-bottom wing enables slower landings, and its position high on the fuselage with dihedral provides nearly hands-off upright stability.


1. A flat-bottom wing with a curved top surface produces significant lift (the low-pressure vacuum supporting the airplane’s weight) as air flows over it. This enables a basic trainer to fly at slower airspeeds.
2. A thicker airfoil with greater curvature generates more lift to allow flying (and landing) at slow speeds.
3. A high-wing location on top of the fuselage places the lift support above the airplane’s CG. Similar to a parachute supporting the person below, a high-wing airplane wants to stay upright, and if rolled inverted, this type will eventually right itself with enough time and altitude.
4. Wing dihedral improves upright stability by further angling the wing above the CG for a greater parachute or “plumb bob” effect.
5. When stalled, a constant-chord wing loses lift first at the center root, while the airflow remains smooth and continues to provide lift and aileron effectiveness out toward the wingtips. A root stall results in the airplane remaining controllable, and it has a milder sink or mush when flown too slowly (see Figure 2).




Figure 2: The primary features that make a good basic trainer are a thick, flat-bottom airfoil, high wing placement, and constant chord. The thick, flat-bottom wing enables slower landings, and its position high on the fuselage with dihedral provides nearly hands-off upright stability.
A constant-chord wing inherently stalls at the root while the airflow continues to flow smoothly over the outboard portions of the wing. The resulting loss of lift at the root results in a controllable mush or sink, while the tips continue to provide lift and aileron control during a stall.


The chief features of a good primary trainer are a flat-bottom airfoil to enable slow flight and slower landings, a high wing placement to enhance upright stability, and a constant-chord wing to ensure mild, controllable stall characteristics.

Although a primary trainer with ailerons is capable of aerobatics because it is positively stable, the pilot has to work hard to maneuver it through unusual attitudes. It is easier to perform and learn aerobatics utilizing an airplane designed for aerobatics.


Sport/Basic Aerobatic Aircraft Characteristics

Nearly all airplanes with symmetrical wings, minimal dihedral, and ample power are well suited for aerobatics. Assuming that they are trimmed and balanced properly, symmetrical-wing airplanes are mostly neutral. They maneuver nearly as well upside down as they do upright, and are inclined to stay in whatever attitude the pilot puts them in, “as if they are on rails!”

A symmetrical wing typically needs higher speeds to maintain level flight, so when this type is slowed down to set up for a landing, the sink rate tends to be steeper than that of a primary trainer.

A good sport or basic aerobatic airplane features a constant-chord wing that enables it to be slowed or stalled without spinning out of control.

The shoulder-wing variant will still exhibit a slight amount of positive (upright) stability because the wing is positioned slightly above the CG and is easier to fly. The existence of positive stability, however, requires a more vigorous technique to perform aerobatic maneuvers, but it won’t exaggerate overcontrolling.

A shoulder-wing sport airplane is ideal for pilots who are ready to move beyond a basic trainer and learn basic looping and rolling maneuvers without the airplane causing any nasty surprises (see Figure 3).




Figure 3


The advanced mid- or low-wing variant is more neutral because the wing is positioned closer to the CG. This type of aircraft is more maneuverable and is inclined to do precisely what the pilot tells it to do. Modelers must control all aspects of flight with greater finesse because the aircraft will obey improper commands as easily as it follows correct inputs. It’s not more difficult to fly, but there’s a smaller margin for error compared with a high-wing airplane.

A mid- or low-wing sport aerobatic airplane is ideal for pilots who are becoming proficient at basic aerobatics and are looking to fly with greater precision, but want to keep the milder stall characteristics of a constant-chord wing during landings.


Sport Aerobatic Design Features

The primary design features that determine this airplane’s performance are the shape of the wing and its location on the fuselage (see Figure 4).




Figure 4: A good sport airplane will feature a thick, constant-chord, symmetrical wing to make it well suited for looping and rolling maneuvers and prone to staying in whatever attitude you place it. It is also capable of flying/landing slower without exhibiting nasty tendencies (assuming it’s not tail-heavy).


These features include:

1. A semi- or fully symmetrical wing that enhances penetration, furnishes the neutral characteristics that cause the airplane to fly well, and enables it to maneuver nicely in all attitudes.
2. A thicker symmetrical airfoil expands the flight envelope by providing ample lift at slower speeds (high angles of attack), yet when the power and speed are increased, a sport airplane’s capabilities with a thicker symmetrical airfoil increase.
3. A shoulder-wing position slightly above an airplane’s CG causes the model to remain slightly stable and more forgiving when flown upright, at slow speeds, and during inside (pulling) maneuvers. A mid- or low-wing position closer to the aircraft’s CG causes it to be more neutral and more inclined to do precisely what the pilot tells it to do and to perform a variety of precise maneuvers in capable hands.
4. Little or no dihedral also contributes to neutral stability by keeping the overall wing closer to the CG.
5. A constant-chord wing is a critical feature that enables these airplanes—although highly aerobatic—to exhibit forgiving stall characteristics when overcontrolled or flown too slowly.

Thanks to the wide flight envelope permitted by the thick constant-chord symmetrical wing and lower overall wing placement, a good sport airplane is effectively several models in one—offering several levels of crawl-walk-run performance, depending on the speed in which they’re flown and the amount of control surface travel that they are set up with.

Note: A constant-chord wing’s aversion to tip stalling tends to produce less-than-dramatic snap-roll performance. When a pilot is ready to start performing snap rolls and spins, a tapered-wing airplane with its tip-stall characteristic is more suitable (see Figure 5).




Figure 5



Advanced Aerobatic Aircraft Considerations

When a pilot graduates to a fully symmetrical tapered-wing model such as an Extra, Edge, MX, Sukhoi, Yak, etc., there are virtually no limits to what he or she can do. All of these aircraft are equally capable and any differences that are not setup-related are often so small that they are undetectable to all but expert fliers. What remains to be determined is how far the pilot wants to take it, and it will be set up to promote rapid advancement.

When stalled, a tapered wing loses more lift toward the wingtips (see Figure 6). When a large amount of elevator is intentionally applied and a yaw force is also introduced, the tip stall can be exploited to produce snap rolls and spins.




Figure 6: A constant-chord wing stalls at the wing root first, while the wingtips continue to provide lift. Although more forgiving, this wing’s aversion to tip stalling tends to produce a less-than-dramatic snap roll.
The primary feature of an advanced aerobatic model is the fully symmetrical tapered wing for its inherent tip-stall characteristic that can be exploited to achieve excellent snap-roll performance.




This also makes the airplane less forgiving if it is accidently overcontrolled or flown too slowly on landing approach. As the more forgiving qualities of constant-chord airplanes are forfeited for the higher performance of a tapered-wing aircraft, a pilot’s ability to land this type of model must also be considered.

When a tapered wing stalls, both wing halves seldom stall the same, so one wing half will typically drop ahead of the other. This is followed by a snap roll or a spin if the elevator isn’t quickly reduced and/or power isn’t added to increase airspeed.

Although this type doesn’t require any special skills to fly, continued success often comes down to a pilot’s ability to quickly recognize the signs of an impending stall so corrective action can be taken before control is lost.

Pilots transitioning to tapered-wing models need to recognize that inadvertent tip stalls are often preceded by pulling increasing amounts of elevator in an attempt to prevent a steep or slow turn from losing altitude, or to stretch a landing approach. If you ever find yourself steadily increasing the elevator on final approach, or if you are urged to pull more, don’t! You are on the verge of stalling and need to reduce elevator and/or add power to keep from losing control and spinning onto the ground.

The exception to the tip-stall behavior described is when a tapered wing airplane is extremely lightweight. The heavier a model is in proportion to its size, the more important its aerodynamics.

The lighter that an aircraft is, the less critical its aerodynamics are. Some exceptionally lightweight tapered-wing airplanes have such mild stall characteristics that they exhibit virtually no tendency to tip stall. Experience will tell.

Space in this article does not permit me to address all variations of 3-D airplanes, biplanes, and swept-wing aircraft. Know that most symmetrical-wing aerobatic biplanes offer neutral, mid-wing type handling and most swept wings behave similar to tapered wings when stalled.

Also note that “flat-plate” airfoil foamies tend to be highly unstable and difficult to trim, and therefore would not be good choices for inexperienced pilots. Their instability, however, often makes them excellent 3-D performers in the hands of skilled pilots.


Conclusion

A flat-bottom wing airplane allows a pilot more time to think, but has limited capabilities. Symmetrical-wing airplanes offer greater speed, performance, and are less affected by wind, but usually require higher landing speeds. Symmetrical-wing aircraft perform as commanded, so they need to be controlled correctly or they will expose any poor fundamentals that a pilot could otherwise get away with when operating a basic trainer.

Those who cannot comfortably land a basic trainer would find the transition to a faster symmetrical-wing aircraft difficult and mixed with surprises, which are often blamed on radio problems and wind.

On the other hand, if a pilot can comfortably land a trainer—proving good fundamentals—he or she will enjoy stepping up to the “flying on rails” feel and increased capabilities of a symmetrical-wing sport airplane. When he or she is able to comfortably grease every landing with that airplane, again proving good technique, transitioning to a tapered-wing airplane will be a successful and enjoyable experience!

Good luck.
—Dave Scott
1usrcfs@gmail.com


About the Author

Dave Scott is a champion full-scale Aerobatics competitor and an air show pilot who operates a successful commercial RC flight school. His groundbreaking manuals and articles feature the training techniques he developed—instructing more than 1,700 RC pilots of all skill levels and setting up and test-flying approximately 1,000 airplanes at his school. More information about his books and school can be found at www.rcflightschool.com.

Sources:

1st U.S. R/C Flight School
www.rcflightschool.com

3 comments

As a pilot in training, I have found this article quite helpful. It reinforces what I have experienced with simulator practice of various trainer aircraft designs.

Thanks so much for this very helpful article. I am new to the sport but feel as if I have mastered basic/trainer aircraft. I am attending my first RC flea market in March and now have a much better idea of what to look after.

A simple adjustment of the way I looked at the airplane was all I needed. Your comment to me about making the airplane fly the way you want it to changed my outlook. So I've worked the numbers on all my planes and they pretty much fly the same now, in that when I give a certain amount of input I get the expected amount of reaction from the plane. Now my Pandoras, P51s and the Pitts are joys to fly!

Dan

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